Comparison of Seafloor and Shallow Stratigraphic Conditions Mapped From 3D Seismic and AUV Data at Two Deepwater Areas, Keathley Canyon, Gulf of Mexico

Abstract

Abstract This paper presents results of an integrated interpretation effort to understand seafloor and shallow stratigraphic conditions at drill sites within two prospective areas in a deepwater portion of the northern Gulf of Mexico. Datasets of different resolution were utilized, including AUV multibeam echo sounder data. These highest resolution AUV data were collected early in the life of the two projects to assess seafloor conditions. In one instance, the AUV data were acquired to comply with newly issued governmental regulations for archaeological clearance studies. As an added benefit, the required AUV data also provided a clear view of potential seafloor geological constraints giving BP and co-owners early insight into factors such as chemosynthetic community indicators, seafloor expulsion features and hardgrounds. These insights will be used and further developed throughout the life of the projects, affecting work not only during early exploration, but also in an exploration success case, through appraisal, development and into production phases as a baseline survey. The primary purpose of this case study was to learn how geophysical data collected at different resolutions during subsequent project phases could be leveraged to efficiently discern potential constraints to operations resulting from geological processes affecting seabed and near-surface stratigraphy. Additional insight came from a comparison of geological conditions at the two sites. These conditions were similar at the nearby sites but key differences were noted. The steps followed may define a multiphase approach that efficiently uses site survey results and supports early acquisition of detailed site investigation data. In addition to obtaining detailed site investigation data early on, it is shown that obtaining more than the minimum coverage area needed to clear the initial exploration locations in a prospect has the added benefit of providing broader geographic understanding of seafloor conditions away from the prospect center, revealing potential constraints that would affect appraisal and development locations while reducing or eliminating the need for subsequent surveys. A comparison of conditions at the two prospects showed similar geological settings and highlights the different needs for high-resolution site investigation data at different stages of a field development, not just during the development phase, as has been practiced previously. Results of the site investigation evaluation have been incorporated into planning of wellbore trajectories at prospects in the Keathley Canyon protraction area and in documents submitted to comply with regulatory requirements of the Bureau of Ocean Energy Management.